I was reading the documentation for MozRepl and found this:

In cygwin, please add binmode param as 1 in client args.

    $repl->setup({
        client => {
            extra_client_args => {
                binmode => 1
            }
        }
    });
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Is the above relevant to www::mechanize::firefox? How would I implement the above using the functions included in www::mechanize::firefox?

WWW::Mechanize::Firefox uses MozRepl::RemoteObject, which uses MozRepl, so this could be relevant. I don't use Cygwin, so I don't know if this really is relevant.

I think the easiest way is to pass in a preconstructed MozRepl object when constructing the WWW::Mechanize::Firefox object.

OK, I might have just gotten lucky here, but I seem to have fixed the problem. I found two lines in Client.pm that explicitly refer to cygwin:

$command = join(" ", split(/\n/, $command)) if ($^O eq "cygwin");
$args->{extra_client_args}->{binmode} = 1 if ($^O eq "cygwin");
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I commented out both of them and now my script produces the expected output:

title: Google
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When I run the test suite I get a lot of dubious results, but I seem to have fixed the immediate problem.